Hydrodechlorination of trichloroethylene over Pd supported on swellable organically-modified silica (SOMS)

Abstract

The catalytic activity and resistance to poisoning of Pd catalysts supported on swellable organically-modified silica (SOMS) were investigated for hydrodechlorination (HDC) of trichloroethylene (TCE). The promising catalytic activity of 1% Pd/SOMS sample was attributed to the high affinity of SOMS for organics and its high hydrophobicity. While latter characteristic repels water, the adsorptive capacity for organics allows TCE dissolved in aqueous media to concentrate inside the pores, in the vicinity of the active sites, thus helping the kinetics. In the liquid phase, using a continuous flow reactor, higher TCE conversion was obtained over the 1% Pd/SOMS compared to the commercial 1% Pd/Al2O3 catalyst. When the pores of 1% Pd/SOMS sample were fully opened by pre-treating it with ethanol prior to the reaction, HDC activity was seen to significantly increase. In the gas phase, the extent of adsorption was less, reducing the concentration of reactants near the active sites. As a result, 1% Pd/SOMS was less active than 1% Pd/Al2O3 for HDC of TCE. To determine their resistance to poisoning, 1% Pd/SOMS and 1% Pd/Al2O3 catalysts were poisoned ex-situ with Li2S. The ex-situ poisoned Pd/SOMS sample maintained its catalytic activity for HDC of TCE. However, a significant loss in catalytic activity of the Pd/Al2O3 catalyst was observed after poisoning. Protection from aqueous phase sulfide poisoning was attributed to the hydrophobicity of the Pd/SOMS, which would exclude anionic species from the embedded Pd particles. The XPS, STEM and ICP-OES results indicated that when Pd/Al2O3 and Pd/SOMS were treated with 1 M HCl, most of the Pd metal was leached from the Pd/Al2O3 catalyst in contrast to Pd/SOMS, which had negligible leaching. Overall, due to hydrophobicity and high affinity for organics, SOMS has potential as a catalyst scaffold for different reactions in groundwater remediation applications.

Aqueous‐Phase Hydrodechlorination of Trichloroethylene on Ir Catalysts Supported on SBA‐3 Materials

“…Hence, the properties of Ir/SBA‐3 and Ir/AlSBA‐3 in removal of TCE from water could be strongly related with the hydrophobicity of these materials. Additionally, the hydrophobic nature of Ir/AlSBA‐3 and Ir/SBA‐3 acts as a benign protection layer to restrict both the agglomeration or redispersion or leaching effect, as it was confirmed by TEM analysis for spent catalysts (Figure ) …”

“…The activity can be also influenced by hydrophobicity of the catalysts. Based on the literature data hydrophobicity plays beneficial role in protection of active phase from poisoning and leaching and helps the kinetics. Hence, the properties of Ir/SBA‐3 and Ir/AlSBA‐3 in removal of TCE from water could be strongly related with the hydrophobicity of these materials.…”

Effect of high-temperature on the swellable organically-modified silica (SOMS) and its application to gas-phase hydrodechlorination of trichloroethylene

“…Previously, we have reported on a new class of materials, swellable organically-modified silica (SOMS), as catalyst support for Pd used in HDC of TCE. 49 SOMS is an extremely hydrophobic and adsorptive material, which can adsorb various types of organic compounds from air and water. When sufficient adsorption takes place, pore filling can initiate the physical expansion of the SOMS volume, called as "swelling".…”

“…The higher catalytic activity over Pd/SOMS was attributed to the swelling behavior of SOMS, which only adsorbed TCE molecules from the solution (hydrophobicity) and concentrated them in the vicinity of the Pd active sites inside the pores. 49 Additionally, the Pd active sites were protected by the strong hydrophobicity of SOMS from poisoning by sulfur anions dissolved in water. 49 It was observed that the Li 2 S poisoned-1% Pd/SOMS maintained its catalytic activity compared to fresh 1% Pd/SOMS whereas Li 2 S poisoned-1% Pd/Al 2 O 3 catalyst was completely deactivated.…”

“…49 Additionally, the Pd active sites were protected by the strong hydrophobicity of SOMS from poisoning by sulfur anions dissolved in water. 49 It was observed that the Li 2 S poisoned-1% Pd/SOMS maintained its catalytic activity compared to fresh 1% Pd/SOMS whereas Li 2 S poisoned-1% Pd/Al 2 O 3 catalyst was completely deactivated. Also, Pd supported on SOMS was seen to be more resistant to leaching in acidic medium.…”